The enemies I found in the swamp on my way to deliver the griffin head were also much higher leveled than me, though not as bad as in the graveyard. I'll admit it may be possible I just happened to wander into the worst possible areas which wrongfully gave the impression that was the whole game, but it's bad game design regardless if that's even possible. I absolutely despised the clunky combat and broken controls anyway, so I had no desire to play anymore. Fighting the griffin was a nightmare.
It honestly just sounds like you don't understand the combat, and I mean that with sincerity, because I absolutely hate those kind of "u just suck get good scrub" replies. I mean, the levels of the enemies do matter but something 3-6 or so levels above you isn't going to be that much of a challenge(I'm trying really hard to remember like, how many levels above you a monster had to be in order for it to be really difficult to fight). I have a bad condition of constantly replaying the opening of games a lot. I also really suck at games. So I'm not trying to say this from an elitist perspective, but it really isn't that difficult. You might die once or twice but the Witcher isn't about easy combat necessarily. You shouldn't get discouraged from dying once because in most cases it just means you should have pressed the dodge button or had a different spell equipped.
In one of the earliest times I restarted the Witcher, I decided to do every sidequest and mission available at the beginning of the game before activating world traversal. The starting area was really really easy, even though most of it I hadn't explored before. You can even tell what quests CD Projekt Red wanted to naturally integrate into the player's journey, like the Swamp quest which literally is right off the road and just involves you spending two minutes going into a Swamp.
" I'll admit it may be possible I just happened to wander into the worst possible areas which wrongfully gave the impression that was the whole game, but it's bad game design regardless if that's even possible. "
This happened to a pretty well-known reviewer while playing Breath of the Wild. He went to an area behind the starting plateau I believe, and he died numerous times. He actually learned the enemies attack patterns, but because of weapon degradation he couldn't kill off the enemy without losing all his weapons. This makes it even worse than your Witcher example. So is Breath of the Wild a badly designed game?
I don't even think this makes much sense in the context of an open world game. An open world game should have depth in it. It's a living, breathing world that you can traverse. The game didn't make you go there, you did. You can just keep riding away if you don't want to fight, and the wraith literally disappears for a few seconds after an engagement begins so it's easy to get away. If all of the open world was tailor made to make every engagement exactly your level or gratifying, it wouldn't feel like an open world. Now if every corner was filled with enemies 70 levels higher than you, that might be an issue *cough cough Xenoblade 2 cough cough* but that's just not true.
In fact there's a series that gets a lot of acclaim for it's world building based on enemy placement, called Gothic. Personally I've never played it, so maybe vivister will come in here and show me my place or something, but a big part of it's appeal is that if you go down the wrong path and don't come equipped your fucked. It makes it feel like an actual world. But hell, that's such an extreme example, The Witcher 3 isn't even nearly that bad, or hard.
I know that's a pretty long winded reply but i'm not like a Witcher apologist or anything. Honestly I never got around to finishing the game, I'd always get to a certain point and be turned off. I just wanted to add my own two cents in, you don't have to agree.